2009’s Sleepy Sun Finally Woke Up in December

2009 will go down as the sun’s third quietest year on record, under-shone only by 1913 and 2008.

Two hundred-sixty of the year’s 365 days (71 percent) were sunspotless. Last year saw 266 sunspotless days, while the sun had no spots on 311 of the days in 1913. It was only a very active December that kept 2009 from falling below last year’s mark.

Sunspot activity waxes and wanes in a roughly 11-year cycle, so hitting solar minima isn’t surprising. But what the numbers underscore is that we spent much of the year still in the midst of the deepest, longest solar minimum in a long time.

People keep their eyes on sunspots because their frequency and intensity is correlated with the overall level of solar activity. Changes in the sun’s energy flows can seriously impact conditions on Earth and our immediate environment in space. While a particularly active sun can generate geomagnetic storms that damage satellites and electrical grid infrastructure, a sun as quiet as the one of the last few years could affect the Earth’s climate, although not by much.

“If you want to understand all the drivers of Earth’s atmospheric system, you have to understand how sunspots emerge and evolve,” Matthias Rempel of NCAR’s High Altitude Observator told Wired.com for an earlier story.

The science of sunspots is still murky, despite new supercomputer simulations and theories about their formation. The sun remains filled with surprises.

It’s been an erratic year for sun watchers. At first, it appeared that 2009 might be even quieter than 2008. Eighty-seven percent of the days in the first three months of the year were sunspotless. In May, a big solar flare, the strongest of the new cycle, appeared to augur a return to normal for the sun. Then, August was nearly sunspotless. And in the final reversal, December has been far more active than the rest of the year.

Five regions on the sun were active at once on the 22nd, as seen above. Again assuming the current sunspot holds together until Thursday, there will have been at least one spot on 22 of the month’s 31 days.

But Tony Phillips, a NASA sky watcher who made the chart above and sketched the trend line, isn’t quite ready to declare the solar minimum over.

“If the trend continues exactly as shown (prediction: it won’t), sunspots will become a non-stop daily occurance no later than February 2011. Blank suns would cease and solar minimum would be over,” Phillips wrote on Spaceweather.com. “If the past two years have taught us anything, however, it is that the sun can be tricky and unpredictable. Stay tuned for surprises.”